It appears that a "default" cursor theme must be specified in order for a mouse cursor to show.
This theme file is found here: ~/.icons/default/index.theme
This file specifies a mouse cursor theme to be used by default. However, if this file doesn't exist, there is no fallback cursor -- so the cursor remains invisible.
-------------
To replicate:
-------------
Hopefully this will replicate the issue for everyone else:
1) Temporarilly remove/rename the following file:
~/.icons/default/index.theme
2) Run Weston in either direct rendering mode or as an X client.
-------------
Result:
-------------
The mouse cursor should be "invisible".
-------------
Fix:
-------------
Could we set a default cursor if no others are sepcified?
-------------
Info:
-------------
The following bug could in fact be the same issue as the one I've highlighted above:
https://bugs.freedesktop.org/show_bug.cgi?id=51016
For a bit more info, this post on the Arch forums solved the "invisible cursor" bug for me (all credit for the fix goes to user Giselher).
https://bbs.archlinux.org/viewtopic.php?pid=1122238#p1122238